1. Field of the invention
The present invention relates to a battery charging method for hybrid electric vehicles capable of supplementing battery by charging a main motor when the hybrid electric vehicles stop.
2. Description of Related Art
A hybrid electric vehicle (HEV) is generally configured to transfer power to wheels through a continuously variable transmission (CVT) in a form in which an electric throttle control (ETC) is added to an engine and an electric motor is directly connected thereto.
The hybrid electric vehicle is controlled to correspond to traveling conditions so as to make fuel efficiency of the engine highest. Meanwhile, the hybrid electric vehicle is transferred with inertial energy of a vehicle through wheels at the time of braking and deceleration and converts the inertial energy into electric energy through a motor so as to recharge a battery, thereby achieving fuel efficiency higher than that of the existing gasoline engine.
As described above, when charging the battery of the hybrid electric vehicle, there are no cases in which conditions of vehicle speed, deceleration demands, and the like, are instantly same, and as a result, the battery may not be recharged with constant voltage. Further, even when the charging state of the battery is low, generation efficiency needs to be maximized and thus, the charging of the battery with constant voltage applied only in a special case.
Meanwhile, in the case of the existing parallel type hybrid electric vehicle, the battery recharged by a main motor only during the traveling when the remaining capacity of the battery is insufficient and recharged with a small amount by a hybrid starter generator (HSG) rather than by the main motor when the vehicle stops.
That is, as shown in FIG. 1, in the case of the existing parallel type hybrid vehicle, the engine stops when the vehicle stops and the vehicle waits in a state in which an engine clutch is separated. Thereafter, when the vehicle starts again, the engine is ignited and driven. In this case, the battery is recharged by the HSG and the driving RPM of the motor synchronizes with the RPM of the engine and then, the engine clutch is locked and the motor starts.
However, the driving conditions may be variable and therefore, the case in which the remaining capacity of the battery is insignificant may always occur in the hybrid vehicle. In this condition, when the vehicle stops at a drive stage (D stage) as in the past, the charging amount of the battery by the HSG is limited and thus, the battery cannot be fully recharged. The phenomenon hinders the sufficient use of the motor at the time of traveling, which leads to the reduction in the drivability of a vehicle and the fuel efficiency.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.